Ive frequently heard が and げ pronounced as nga and nge. Ive read that this is an older form of pronounciation and that younger people use ga/ge but I seem to comeacross it all the time. Are there any rules of thumb as to where/when one can expect to hear this pronounciation used?

Although I'm not sure if a questioner is still interested in this query or not, I'm going to explain some.
We call it 鼻濁音（びだくおん） that Gg Line with Ng sounds (like Nga Ngi Ngu Nge Ngo).
As a questioner pointed out，鼻濁音 is hardly heard in around Tokyo and South part of Japan. But 鼻濁音 is still used in 東北(Tohoku) area ( North part of 本州 ), even between the young generation.

Rules
・The pronunciation of the words beginning with ガギグゲゴ never become 鼻濁音.
( がっこう＝学校 、げんざい＝現在、ぎんこう＝銀行 are not pronounced with 鼻濁音 )
・Originally, Particle 「 が」 is 鼻濁音.
( like 嵐 が きた。 ) ( 花 が 咲いた)
・In the case of an onomatopoeia, and a Chinese word, it will not become
鼻濁音。
(ガクガク、グズグズ、ゲラゲラ 、侃々諤々＝カンカンガクガク）

Mostly, 演歌 singers, 歌舞伎/ actors master 鼻濁音.
Great 演歌 singers use accurate 鼻濁音 commonly.
If you listen the song named 『 津軽海峡冬景色＝つがる かいきょう ふゆげしき』 sung by 石川さゆり,You will notice which is 鼻濁音.
She sings with using 鼻濁音, like「つカ°る かい きょう ふゆ ケ°しき」.

In phonetics, usually phonetic signs (カ°キ°ク°ケ°コ°)are used to distinguish from other ガギグゲゴ.

Yes, you are right. If you don't have any ambition to become an 演歌singer,
you don't have to learn 鼻濁音. Even announcers/anchorman, it is rare to pronounce exact 鼻濁音.
(and neither can I. )
They say 鼻濁音 will disappear one of these days.

Last edited by coco on Tue 11.22.2005 11:54 pm, edited 1 time in total.